310 research outputs found
Ab-initio-calculations of the GMR-effect in Fe/V multilayers
In a self-consistent semi-empirical numerical approach based on
ab-initio-calculations for small samples, we evaluate the GMR effect for
disordered (001)-(3--Fe/3--V) multilayers by means of a Kubo
formalism. We consider four different types of disorder arrangements: In case
(i) and (ii), the disorder consists in the random interchange of some Fe and V
atoms, respectively, at interface layers; in case (iii) in the formation of
small groups of three substitutional Fe atoms in a V interface layer and a
similar V group in a Fe layer at a different interface; and for case (iv) in
the substitution of some V atoms in the innermost V layers by Fe. For cases (i)
and (ii), depending on the distribution of the impurities, the GMR effect is
enhanced or reduced by increasing disorder, in case (iii) the GMR effect is
highest, whereas finally, in case (iv), a negative GMR is obtained (''inverse
GMR'').Comment: LaTex, 30 pages, including 16 drawings; to appear in JMM
Berry curvature unravelled by the Nernst effect in MnGe
The discovery of topological quantum materials represents a striking
innovation in modern condensed matter physics with remarkable fundamental and
technological implications. Their classification has been recently extended to
topological Weyl semimetals, i.e., solid state systems which exhibit the
elusive Weyl fermions as low-energy excitations. Here we show that the Nernst
effect can be exploited as a sensitive probe for determining key parameters of
the Weyl physics, applying it to the non-collinear antiferromagnet MnGe.
This compound exhibits anomalous thermoelectric transport due to enhanced Berry
curvature from Weyl points located extremely close to the Fermi level. We
establish from our data a direct measure of the Berry curvature at the Fermi
level and, using a minimal model of a Weyl semimetal, extract for the first
time the Weyl point energy and their distance in momentum-space
Extremely high magnetoresistance and conductivity in the type-II Weyl semimetals WP2 and MoP2
The peculiar band structure of semimetals exhibiting Dirac and Weyl crossings
can lead to spectacular electronic properties such as large mobilities
accompanied by extremely high magnetoresistance. In particular, two closely
neighbouring Weyl points of the same chirality are protected from annihilation
by structural distortions or defects, thereby significantly reducing the
scattering probability between them. Here we present the electronic properties
of the transition metal diphosphides, WP2 and MoP2, that are type-II Weyl
semimetals with robust Weyl points. We present transport and angle resolved
photoemission spectroscopy measurements, and first principles calculations. Our
single crystals of WP2 display an extremely low residual low-temperature
resistivity of 3 nohm-cm accompanied by an enormous and highly anisotropic
magnetoresistance above 200 million % at 63 T and 2.5 K. These properties are
likely a consequence of the novel Weyl fermions expressed in this compound. We
observe a large suppression of charge carrier backscattering in WP2 from
transport measurements.Comment: Appeared in Nature Communication
NSCG-Kommission 'Curriculum Chemie': Eine Bestandesaufnahme über Studium, Promotion und Berufsaussichten junger Chemikerinnen und Chemiker von 1992–1996 (Statistischer Teil)
Somatostatin subtype-2 receptor-targeted metal-based anticancer complexes
Conjugates of a dicarba analogue of octreotide, a potent somatostatin agonist whose receptors are overexpressed on tumor cells, with [PtCl 2(dap)] (dap = 1-(carboxylic acid)-1,2-diaminoethane) (3), [(η 6-bip)Os(4-CO 2-pico)Cl] (bip = biphenyl, pico = picolinate) (4), [(η 6-p-cym)RuCl(dap)] + (p-cym = p-cymene) (5), and [(η 6-p-cym)RuCl(imidazole-CO 2H)(PPh 3)] + (6), were synthesized by using a solid-phase approach. Conjugates 3-5 readily underwent hydrolysis and DNA binding, whereas conjugate 6 was inert to ligand substitution. NMR spectroscopy and molecular dynamics calculations showed that conjugate formation does not perturb the overall peptide structure. Only 6 exhibited antiproliferative activity in human tumor cells (IC 50 = 63 ± 2 μ in MCF-7 cells and IC 50 = 26 ± 3 μ in DU-145 cells) with active participation of somatostatin receptors in cellular uptake. Similar cytotoxic activity was found in a normal cell line (IC 50 = 45 ± 2.6 μ in CHO cells), which can be attributed to a similar level of expression of somatostatin subtype-2 receptor. These studies provide new insights into the effect of receptor-binding peptide conjugation on the activity of metal-based anticancer drugs, and demonstrate the potential of such hybrid compounds to target tumor cells specifically. © 2012 American Chemical Society
- …